A brush seal device 100 shown in FIG. 15 is based on an art related to the present invention.
FIG. 15 is a cross-sectional view of a brush seal device 100 mounted in a fitting portion between a casing 120 and a rotational shaft 130, for example, of a steam turbine. FIG. 16 is a plan view of the inner periphery of a connecting portion of the brush seal device shown in FIG. 15.
In FIGS. 15 and 16, when the brush seal device 100 is installed between bearings of the steam turbine, brush seal split parts 101, into which the brush seal device 100 is divided, are connected to one another and assembled into an annular body surrounding the rotational shaft 130, without removing the rotational shaft 130 or the bearings. Each of the brush seal split parts 101 has connecting portions at its opposed ends and is connected at the connecting portions to adjacent ones of the brush seal split parts 101.
Even in the case where the rotational shaft 130 has a large diameter, since the brush seal device 100 is designed as a split type, sequential assembly of the brush seal split parts 101 makes it unnecessary for a large number of operators to perform the assembling operation while hoisting a bulky annular brush seal device by means of a crane or the like.
The brush seal device 100 is mounted in a mounting groove 121 formed in the casing 120. The brush seal device 100 is pressed inwards in a springy manner from the outer periphery side by a leaf spring (not shown). Therefore, a space portion 122 exists between the outer peripheral surface of the brush seal device 100 and the surface in which the mounting groove 121 is formed.
A multitude of bristles 103 are disposed in a wall shape along the inner periphery of the brush seal device 100 as shown in FIG. 17, which illustrates another related art. The outer periphery of a brush seal 102 composed of the bristles 103 is mounted to a mounting portion 104. The brush seal 102 is disposed slantingly and is designed to be opposed to a rotational shaft (not shown).
The mounting portion 104 of the brush seal 102 is fixed to a back plate 105. The brush seal 102 is designed, in a region ranging from the mounting portion 104 to its free end, to be supported by the back plate 105 and not to be deformed substantially even if sealed fluid acts thereon from the side of a pressure P1. A holding plate 107 fixes the mounting portion 104 of the brush seal 102 together with the back plate 105 by welding. As shown in FIG. 16, the brush seal split parts thus constructed are arranged in the circumferential direction at intervals of one-sixth of the circumference.
Each of these brush seal split parts is in the shape of an arc and has splitting surfaces 110 at its opposed ends. Each of the splitting surfaces 110 of each of the brush seal split parts is connected to the splitting surface 110 of another corresponding one of the brush seal split parts, so that an integral-type annular body is formed. Each of the splitting surfaces 110 is composed of axial surfaces 111 and a radial surface 112 and thus assumes a step-like structure.
When these brush seal split parts are in a mounted state, the splitting surfaces 110 are joined to one another. However, as shown in FIG. 16, the axial surface 111 of the brush seal device 100 allows a narrow gap C1 to be created due to an operational force resulting from oscillation of the rotational shaft 130 or the like. In such a case, sealed fluid on the side of the high pressure P1 flows through the gap C1 on the side of the high pressure P1, reaches the space portion 122, flows through a gap C2 on the side of a low pressure P2, and leaks out to the side of the low pressure P2.
FIG. 17 shows the brush seal device according to another related art. FIG. 17 is a side view of a connecting portion 109 of the brush seal device 100. FIG. 18 is a plan view of the brush seal device 100 shown in FIG. 17 as viewed from its inner-diameter side in the direction of an inclining gap C3.
The brush seal device 100 shown in FIG. 17 has the splitting surfaces 110 that are formed in the connecting portion 109 in such a manner as to incline with respect to the radial direction. Even in the case of the splitting surfaces 110, if adjacent ones of the brush seal split parts are displaced in opposite directions, the gap C3 is widened. Then, sealed fluid leaks out from the gap C3.
In the related arts described above, the gap C between the splitting surfaces 110 is widened if the operational force of the rotational shaft 130 or the pressure P1 of sealed fluid is directly applied to the brush seal device 100. Thus, sealed fluid leaks out to the side of the low pressure P2 through the gap C. In particular, if the brush seal device 100 wobbles during rotation as a result of oscillating or swaying movements of the rotational shaft 130, the rotational shaft 130 comes into tight contact with the brush seal device 100. When the rotational shaft 130 is in contact with the brush seal device 100, the former applies an operational force to the latter. This operational force widens the gap between the splitting surfaces 110, 110. As a result, the sealing performance deteriorates to such an extent that sealed fluid leaks out from the gap between the splitting surfaces 110, 110. Therefore, deterioration of the ability to seal the gap between the splitting surfaces 110 looms as a serious problem.
Although the split-type brush seal device 100 is most preferably designed to be held in a springy manner from the outer peripheral side by a leaf spring or the like so as to counterbalance the effect of oscillation of the rotational shaft 130 or the like, the problem of leakage of sealed fluid from the gap C between the splitting surfaces 110, 110 makes it difficult to adopt such a construction in an effective way. Consequently, a large operational force that may be applied to the brush seal 102 from the rotational shaft 130 causes a problem of abrasion of the brush seal 102 at an early stage of its use.
The present invention has been made as countermeasures against the problems as described above. One technical aim of the present invention as a solution to the problems is to prevent leakage of sealed fluid through a gap between splitting surfaces of adjacent ones of brush seal split parts even if the gap has been widened.
Another technical aim of the present invention is to allow adoption of an excellent mechanism for preventing abrasion of bristles not only by the elastic force of the brush seal but also through elastic enlargement or reduction of the diameter of the brush seal split parts constituting an annular body.